The corrosion, transport and deposition of copper and mixed copper-iron materials in steam generating systems is a major problem in industry today. These deposits can result in reduced reliability, damage to the systems, loss of effectiveness and increased costs due to cleaning, unscheduled outages and replacement of equipment.
Even under optimum boiler feedwater and condensate conditions, low dissolved oxygen, and controlled pH, copper oxides will be released as particulate oxides, soluble Cu(I)/Cu(II) and metallic copper species. Copper oxides are relatively unstable and can dissolve, break-up and continually re-deposit within a boiler system.
Deposit control agents are often added to feedwaters of boilers. They act to control the deposition of copper in one of two ways: A solubilization mechanism, where chelants or chelant type molecules, form soluble complexes with the copper which are removed during blowdown; and, a dispersion mechanism, where the deposit control agent adsorbs on surfaces which blocks the adhesion of copper on heat transfer surfaces.
Polymer dispersants are used to disperse particulate matter or solid or colloidal matter already present. To some extent, polymers can also act as chelants to solubilize cations.
Chelants are the prime additives in a solubilizing boiler water treatment program. Chelants have the ability to complex and prevent the deposition of many cations (hardness and heavy metals) under boiler water conditions. They accomplish this by locking the metal into a soluble complex structure. When applied with a dispersant, chelants will result in clean waterside surfaces.
Historically, NTA (Nitrilo Triacetic Acid) and EDTA (Ethylenediaminetetraacetic Acid) were generally considered the most suitable boiler water treatment chelants.